First, a spread spectrum in a wireless is described below. Usually, a communication using the spread spectrum technology is as follows: a modulated input baseband signal for sound or like is modulated at a transmitting end thereby preparing a modulation signal; the modulation signal is subjected to spectrum spreading by using a spreading code at the transmitting end, thereby preparing a spread spectrum signal; and then the spread spectrum signal is transmitted as a high frequency signal to a receiving end reception-performing communication counterpart), which is a communication counterpart of the transmitting end (transmission-performing communication counterpart). The spread spectrum signal sent from the transmitting end, which is a communication counterpart of the receiving end, and received by the receiving end, is then demodulated (despread) at the receiving end, by using the same spreading code used in the transmittance end.
Direct Sequence Spread Spectrum (Hereinafter referred to as “DSSS”) and Frequency Hopping Spread Spectrum (Hereinafter referred to as “FHSS”) are known as communication methods using the spread spectrum. DSSS spreads a signal over a continuous frequency band, by widely spreading the signal of a narrowband modulation wave by multiplying the signal by using a spreading code. FHSS, such as Bluetooth (registered trademark), spreads a signal within a frequency band by randomly switching over frequencies of a carrier wave within the frequency band in accordance with the diffusion code, the carrier wave being used in communication with the communication counterpart.
The following describes a conventional card type wireless communication apparatus. FIG. 21 is a block circuit diagram showing schematic configuration of the conventional card type wireless communication apparatus. The conventional card type wireless communication apparatus 50 shown in FIG. 21 is so configured that an antenna 51 is connected to a receiver circuit 52, and to a transmitter circuit 57.
The receiver circuit 52 includes an amplifier 53, a mixer circuit 54, and a demodulator circuit 55. The antenna 51 is connected to a baseband signal processing circuit 61 through the amplifier 53, the mixer circuit 54 and the demodulator circuit 55.
The transmitter circuit 57 includes a modulator 60, a mixer circuit 59, and an amplifier 58. The baseband signal processing circuit 61 is connected to the antenna 51 through the modulator 60, the mixer circuit 59, and the amplifier 58. The mixer circuit 54 and the mixer circuit 59 are connected to a local oscillator 56.
Further, the baseband signal processing circuit 61 is connected to a connector 65 through an interface circuit 62, and the receiver circuit 52, the transmitter circuit 57, and the baseband signal processing circuit 61 are connected to a circuit control section 63. A power supply 64 is connected to the connector 65 and each of the above-described circuits in the card type wireless communication apparatus 50.
Next described is operation of the conventional card type wireless communication apparatus 50 shown in FIG. 21. A spread spectrum signal (e.g. 2.4 GHz-band) from the communication counterpart (that is, the transmitting end) is received by the antenna 51 of the receiving end. Then, in the receiving end, the spread spectrum signal is amplified by the amplifier 53, and is applied to the mixer circuit 54. The spread spectrum signal, which is the thus received high frequency signal, is demodulated to a baseband signal by the mixer circuit 54 and the demodulator circuit 55. The baseband signal then undergoes a necessary signal processing conducted by the baseband signal processing circuit 61, and is output through the interface circuit 62 and the connector 65 to an information terminal device (not shown), such as a personal computer (PC) or the like.
At the transmitting end, a data signal being inputted from the information terminal device (not shown) through the connector 65 and the interface circuit 62 undergoes the necessary signal processing conducted by the baseband signal processing circuit 61, and is spread to a spread spectrum signal (e.g. 2.4 GHz-band) by the modulator 60 and the mixer circuit 59. The data signal is then amplified by the amplifier 58, and is transmitted via the antenna 51 to the communication counterpart (that is, the transmitting end).
The circuit-control section 63 controls the operation of the receiver circuit 52, the transmitter circuit 57, and the baseband signal processing circuit 61. The power supply 64 receives power through the connector 65 from the information terminal device (not shown) such as a PC or the like, and supplies power+B to each circuit described above in the card type wireless communication apparatus 50.
The local oscillator 56 generates necessary frequency signals (e.g. 2.4 GHz) for the operation of each of the mixer circuits 54 and 59.
For controlling an RF signal of a wireless section, different types of communication apparatuses modulate and demodulate signals of different frequencies and levels after converting the frequencies of the signals. Therefore, it is necessary to have a stable modulation and demodulation characteristics.
Here, one of most important factors is an input dynamic range. The input dynamic range indicates a range of a weakest input signal to an input strongest signal that can be stably received and demodulated.
For the wireless communication apparatus having the receiver and transmitter circuits, the dynamic range is determined mainly by parameters such as transmission (high frequency) power, reception sensitivity, and a distortion property.
There has been desire for a larger communication range. For a short distance communication (in which a distance between a host and a client is short), one of conventional arts for attaining a large communication range is to prevent deterioration in distortion property with respect to a strong incoming signal by using an attenuator in an input stage of a receiver device, or by lowering a gain of a low-noise amplifier or an IF amplifier (see Reference 1: Japanese Publication of Utility Model, Jitsukaihei, No. 4-116440 (published on Oct. 29, 1992))
FIG. 22 shows an example of the conventional art. In FIG. 22, an attenuator circuit (RF ATT) 90 is provided in between a high frequency signal input terminal 71 and a high frequency amplifier 78. The attenuator circuit (RF ATT) 90 includes PIN diodes 91, 92, and 93. The PIN diodes 91, 92, and 93 can be used at RF-band.
In this example, the PIN diodes 91, 92, and 93 arranged in π-shape are (turned ON and OFF in accordance with a switching signal from a terminal 77 depending on whether the high frequency signal is strong or weak. Thereby, the PIN diodes 91, 92, and 93 perform high frequency attenuation when turned ON, whereas the PIN diodes 91, 92, and 93 are in a “through” state when turned OFF.
Note that in FIG. 22, there are provided a high frequency bandpass filter (RFBPF) 79, a mixer (MIXER) 80, a first voltage-controlled oscillator (VCD1) 81, a first IF amplifier (IFAMP) 82, an IF bandpass filter 83, a second IF amplifier 84, an FM detector (FMDET) 85, a second voltage controlling oscillator 86, and an output terminal 87 for outputting a detected signal. Descriptions for these circuits are omitted, as they are well-known circuits. Further, in some cases, the attenuator circuit 90 in FIG. 22 is provided in between the high frequency amplifier 78 and the RFBPF 79 or the mixer 80.
In the conventional art shown in FIG. 21, the power is supplied to the power supply 64 of the card type wireless communication apparatus 50 through the connector 65 from the information terminal device (not shown) such as a PC or the like. There will not be any problems as long as the information terminal device such as a PC or the like operates with power from a commercial power source.
However, when the information terminal device such as a PC or the like operates in order to use the information terminal device such a PC or the like in a mobile manner), the information terminal device is operated with power supplied from a battery mounted in a main body of the information terminal device. Accordingly, the power supply 64 of the card type wireless communication apparatus 50 is supplied, through the connector 65, with the power from the battery mounted in the main body of the information terminal device such as a PC or the like.
Namely, an increase in the power consumption in the card type wireless communication apparatus 50 causes a faster consumption of the battery mounted in the main body of the information terminal device. This shortens a time period (duration of battery) in which the information terminal device can be used without the commercial power source.